Human herpes simplex viruses (HSV-1 and HSV-2) cause significant morbidity and mortality in neonatal and immunocompromised populations. HSVs are cytolytic viruses which have profound impacts on their host cells. The broad, long-term objective of our research program is to understand the regulation of HSV infection in human cells. This research plan focuses on two representative, highly modified HSV proteins. The hypothesis being tested is that viral protein modification acts as a means to regulate HSV replication. The goal of the first specific aim is to use a combination of molecular genetics and cell biology techniques to determine the function of modified, nuclear VP22 during HSV infection. In the second specific aim, the goal is to combine genetic and physical biochemical analyses to correlate ICP22 posttranslational modifications with its function as a regulator of HSV replication. These studies will determine whether viral protein modifications are necessary processes in the replication of HSV. Since the focus is on key features of virus-host interactions, our findings are of importance to studies of other related human viruses. In the long term, this research will help define the molecular basis of regulation of the life cycle of these important human pathogens.